sparc64: Fix array size reported by vmemmap_populate()

vmemmap_populate() attempts to report the used index and total size of
vmemmap_table, but it wrongly shifts the total size so that it is
always shown as 0.

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>